Evaluation of stress distributions of calcium silicate-based root canal sealer in bulk or with main core material: A finite element analysis study.

This research aimed to assess the stress distribution in lower premolars that were obturated with BioRoot RCS or AH Plus, with or without gutta percha (GP), and subjected to vertical and oblique forces. One 3D geometric model of a mandibular second premolar was created using SolidWorks software. Eight different scenarios representing different root canal filling techniques, single cone technique with GP and bulk technique with sealer only with occlusal load directions were simulated as follows: Model 1 (BioRoot RCS sealer and GP under vertical load [VL]), Model 2 (BioRoot RCS sealer and GP under oblique load [OL]), Model 3 (AH Plus sealer with GP under VL), Model 4 (AH Plus sealer with GP under OL), Model 5 (BioRoot RCS sealer in bulk under VL), Model 6 (BioRoot RCS in bulk under OL), Model 7 (AH Plus sealer in bulk under VL), and Model 8 (AH Plus sealer in bulk under OL). A static load of 200 N was applied at three occlusal contact points, with a 45° angle from lingual to buccal. The von Mises stresses in root dentin were higher in cases where AH Plus was used compared to BioRoot RCS. Furthermore, shifting the load to an oblique direction resulted in increased stress levels. Replacing GP with sealer material had no effect on the dentin maximum von Mises stress in BioRoot RCS cases. Presence of a core material resulted in lower stress in dentin for AH Plus cases, however, it did not affect the stress levels in dentin for cases filled with BioRoot RCS. Stress distribution in the dentin under oblique direction was higher regardless of sealer or technique used.

Influence of long -term thermal cycling and masticatory loading simulation on bond strength of roots filled with epoxy resin and calcium silicate based sealers.

BACKGROUND: The aim of this study was to evaluate the effect of thermal and mechanical cyclic aging using a mastication simulator on push-out bond strength of mandibular premolars obturated with AH Plus and BioRoot RCS root canal sealers. METHODS: With REVO-S files up to SU/0.06 taper, 48 single-rooted premolar teeth were instrumented. The teeth were randomly divided into two main groups (n = 24) based on the two root canal sealers used (AH Plus and BioRoot RCS). All teeth were obturated with h matched-taper single-cone. Each main group was then subdivided into three subgroups (A, B, and C) (n = 8). Group A served as the negative control group (no-thermocycling aging). While groups B and C were subjected to thermal changes in a thermocycler machine (15,000 and 30,000 thermal cycles, respectively), followed by two different dynamic loading periods, 3 × 105 and 6 × 105 in a masticatory simulator with a nominal load of 5 kg at 1.2 Hz which represent roughly 1½ and 3 years of clinical function respectively. 2 mm slice at 3 levels, apical, middle, and coronal, to obtain 3 sections were prepared and subjected to push-out test using a universal testing machine. Statistical analysis was performed using analysis of variance (ANOVA) followed by a Tukey post hoc comparisons test and an independent T-test. A significance level of 5% was used. RESULTS: After thermal-mechanical cyclic aging, the two root canal sealers showed a significantly decreased in push-out bond strength (p < 0.05), however, AH Plus had significantly higher bond strength values than BioRoot RCS after cycling aging. CONCLUSIONS: It could be concluded that thermal-mechanical cyclic aging had a significant impact on the outcome of the dislodgment resistance of AH Plus and BioRoot RCS.

Is microbial adhesion affected by the build orientation of a 3-dimensionally printed denture base resin?

STATEMENT OF PROBLEM: How the build orientation of a 3-dimensionally (3D) printed denture affects microbial adhesion is unclear. PURPOSE: The purpose of this in vitro study was to compare the adherence of Streptococcus spp. and Candida spp. on 3D-printed denture bases prepared at different build orientations with conventional heat-polymerized resin. MATERIAL AND METHODS: Resin specimens (n=5) with standardized 28.3 mm2 surface area were 3D printed at 0 and 60 degrees, and heat-polymerized (3DP-0, 3DP-60, and HP, respectively). The specimens were placed in a Nordini artificial mouth (NAM) model and exposed to 2 mL of clarified whole saliva to create a pellicle-coated substratum. Suspensions of Streptococcus mitis and Streptococcus sanguinis, Candida albicans and Candida glabrata, and a mixed species, each at 108 cfu/mL were pumped separately into the model for 24 hours to promote microbial adhesion. The resin specimens were then removed, placed in fresh media, and sonicated to dislodge attached microbes. Each suspension (100 µL) was aliquoted and spread on agar plates for colony counting. The resin specimens were also examined under a scanning electron microscope. The interaction between types of specimen and groups of microbes was examined with 2-way ANOVA and then further analysis with Tukey honest significant test and Kruskal-Wallis post hoc tests (α=.05). RESULTS: A significant interaction was observed between the 3DP-0, 3DP-60, and HP specimen types and the groups of microbes adhering to the corresponding denture resin specimens (P<.05). The difference was statistically significant among 3DP-0, 3DP-60, and HP specimens (P<.05). The adherence of candida was 3.98-times lower on the 3DP-0 than that of HP (P<.05). However, adherence of the mixed-species microbes and streptococci on the 3DP-60 were 1.75 times and 2-fold higher, respectively (P<.05). The scanning electron micrographs showed that 3DP-0 exhibited the lowest microbial adherence compared with HP and 3DP-60. CONCLUSIONS: Adherence affinity of denture base resin is affected by the build orientation rather than by the group of different microbes. Three-dimensionally printed denture base resin fabricated at a 0-degree build orientation exhibited low affinity for microbial adhesion. Three-dimensionally printed dentures may reduce microbial adhesion when printed at a 0-degree build orientation.

Undergraduate dental students' perspective of online learning and their physical and mental health during COVID-19 pandemic.

BACKGROUND AND OBJECTIVE: COVID-19 pandemic continuously spread exacerbating global concerns. It had impacted all life aspects such as social, cultural, economic and education. This study assess the impact of COVID-19 pandemic on undergraduate dental students at Faculty of Dentistry, University of Malaya. The objective of this study is to evaluate the impact of the pandemic on physical and mental health of undergraduate dental students. METHODS: This is a cross-sectional study. An online questionnaire was administrated to 150 undergraduate dental students. The questionnaire included questions related to students' demographic data, their concerns on academic achievement, their opinion on institution response, and the impact of the crisis on their mental and physical health. SPSS software v26.0 was used to analyse the collected data. RESULTS: A total of 147 respondents participated in the study. About 66% of the students felt comfortable in adapting to the new technology while 85.7% were concerned about the quality of online learning. Almost all students 98.6% expressed their doubts on the ability to pass the competency exams and to graduate on time, with only 49.7% agreed that clinical experience was effectively delivered through online classes. Most students were also concerned on the impact of the pandemic on their physical and emotional health 85.8% and 76.9% respectively. CONCLUSIONS: The findings of our study highlight the positive adaptation of the students to online learning and using technology. On the other hand, the study indicates that the COVID-19 pandemic brings negative impacts on our students' physical and mental health.